Today we are going through a phase where processor technologies are improving continuously and as a result we can now get a powerful server in just a couple of Lakhs. And it is so powerful that if you had bought it ten years back, it would have been amongst the top only 2 U of a server rack. This has all been made possible because of the availability of multi-core processors. Today, if you buy a server with a dual Xeon, you get either the power of eight or four Xeon processors, depending on whether you bought a quad core or dual core server. Such a server not only gives you commendable results in number crunching operations but also help you in consolidating your datacenter. For example, the new age processors with multi-core technology provide you with Virtualization a given virtualized OS (which is essentially a Server) and host 7 different server OSes on a single 2 U of a dual Quad-core server. We say 7 instead of 8, as we assume that one core would be used for the host server running the virtualization application.
You might wonder that if one is going to host 7 full-fledged servers running on top of it? Well, rest assured, these servers are not only capable enough to take a huge amount of processing load but can also support RAM of different capacities, starting from 8GB to 64GB. This is enough to host any kind of application, including resource hungry virtualization setups.
Another happening segment related to servers is storage. This segment has essentially two concepts which are gaining importance rapidly. The first is the penetration of Serial Attached SCSI (SAS) hard-disk. Since long SCSI was the de facto standards for Server Direct Attached Storage (DAS). But, due to certain limitations such as the maximum number of disks per channel and total throughout, SAS is taking its place today. The second concept that is gaining importance is the use of Host Bus Adapter (HBA) cards. These are the cards that connect the Host (computer) to storage over iSCSI, Fiber channel, etc. Now let’s discuss all of the above points in detail.
How much RAM?
When choosing a hardware configuration, remember that each application has a different requirement. For instance, if you plan to use your server as a Web Server with lot of static content (such as a Web Portal) or as a file or networked server, then the amount of RAM doesn’t really matter much, assuming you have at least 4 GB RAM. This has become standard nowadays. We came to this conclusion after running our set of I/O, disk and Web benchmarks, on the same server, with 4 GB and 8 GB RAM. In case of Web requests, the performance was the same for both configurations, while in case of file server I/O, the performance improved by 10% with higher RAM. That’s hardly an increment worth spending for extra RAM.
What matters the most in these cases are disk and network speed. Once again, while testing the servers, we noticed that when you stress a server’s disk access performance over the network, then the first thing to get chocked is your Gigabit Ethernet card. This result in data transfer speeds of just below 1,000 Mbps .To rectify this, we joined two Ethernet cards while running network based benchmarks. Such an arrangement gave us double the bandwidth. So here’s a tip: Before thinking of upgrading your processor or RAM for I/O intensive applications, first try
teaming the free LAN cards.
Which Hard Drive?
Another important parameter for I/O intensive networked servers is hard disk performance. This is also critical for database servers. But to get optimum performance, you require a very high capacity hard disk with maximum rpm and throughput, and that too in large numbers. You can actually get better performance out of five 10,000 rpm SATA HDDs than what you can get from two 15,000 rpm SAS drives. But it depends on how much you can spend and what’s more important for you. If redundancy is not important and you have three HDDs, then you can connect all of them in RAID 0 (Stripping mode) and get some really extraordinary performance.
Now, if redundancy is extremely important, which is the case with most users, you can go for RAID 5 with more hard disks (let’s say 6 instead of 3) so that you can reduce the performance degradation while writing parity information, and get performance which is equivalent to having two disks in RAID 0
Expandability
With the growing need of users and organization, one of the vital decisions while buying a server would be the expandability. A server should have enough options for expandability should the need arise in the future. As user needs are growing, so is the data. So storage capacity is one of the most expandability options. What is the maximum number of disks the server allows you to add?
We have seen that a maximum of 8 drive slots are available in a server, while some offer 6 drive slots and 4 is standard across others. An SAS (Serial Attached SCSI) can accommodate up to 1600 plus devices in one channel compared to SCSI which can accommodate only 32. SAS uses serial communication instead of parallel method and hence is capable of providing higher speed data transfer. So SAS is preferred over SCSI nowadays. As far as SATA in concerned it offers lesser expansion in terms of number of disks. External SCSI connectors enable you to connect external SCSI devices like tape drives without need to open the server cabinet for connecting it.
You also need to consider how many DIMM slots are supported by the server as they help you to add additional RAM, so if your server supports 16 GB of RAM but there are only 4 DIMM slots available that means you need to plug a 4 GB RAM in each of the slot, which might be an expensive affair. So more the number of DIMM slots, better it is. Also PCI-X (64-bit) slots help you to add additional fiber channels or RAID cards, which you might include as the need arises. Hence you are also required to consider the number if free PCI-X slots available. RAM upgrade capability of a server can go up to a maximum of 64 GB, while some offer 32 GB, 16 GB upgradability was common across most of them. Any server providing less than 16 GB of RAM upgrade option is not worth the deal, as more and more applications are becoming memory hungry and sooner than later you will require higher RAM support.
Now with Quad Core already available in the market, processor upgradeability is an option that must not be neglected.
HBAs (Host Bus Adapters) are one of the most sought options in servers. Though not many vendors provide it as a default option, still it can be additionally added and it helps you to add host system to other network and storage devices. We have mainly looked into fiber optic HBA which acts as gateway to external SAN, though there are other types as well like ATA, SAS/SATA, eSATA etc.
